1. Field of the Invention
This invention relates generally to a hydrodynamic coupling apparatus for transmitting torque between driving and driven elements by dynamic fluid action.
2. Description of the Related Art Including Information Disclosed under 37 CFR 1.97 and 1.98
Hydrodynamic couplers that transmit torque between driving and driven elements by dynamic fluid action are known in the art. Also known are hydrodynamic coupling apparati that include magnetorheological fluid in a case between a driving element and a driven element. In such apparati an electromagnetic field generator is supported adjacent the case and is positioned to generate a magnetic field within the case and through the magnetorheological fluid to adjust the amount of torque transferred from the driving element to the driven element by adjusting the viscosity of the magnetorheological fluid. Magnetorheological fluid includes magnetic particles suspended within a carrier fluid and is in a liquid state when exposed to little or no magnetic field. When exposed to a magnetic field of increasing strength or flux density the magnetorheological fluid behaves as a Bingham solid, increasing in viscosity through rheological transformation. This occurs because the suspended magnetic particles migrate toward and along lines of magnetic flux to form chains.
An example of such an apparatus is disclosed in U.S. Pat. Nos. 5,779,013 and 5,845,753 issued 14 Jul. 1998 and 8 Dec. 1998, respectively, to Bansbach. Each of the Bansbach patents discloses a hydrodynamic coupling apparatus in the form of a torque transfer device for four-wheel-drive vehicles. Bansbach discloses the torque transfer device as including a transfer case and an input shaft having a first end rotatably supported within the transfer case and a second end connectable to a torque generator. The torque transfer device of the Bansbach patents also includes a driving element fixed to the first end of the input shaft and rotatably supported with the input shaft in the case. A driven element is rotatably supported in the case adjacent the driving element. Magnetorheological fluid is disposed within the case and between the driving element and the driven element and an electromagnetic field generating coil is supported adjacent the case where it generates a magnetic field in the magnetorheological fluid. The electromagnetic field flux density is adjusted to vary the amount of torque transferred from the driving element to the driven element.
Also, U.S. Pat. No. 5,823,309 issued 20 Oct. 1998 to Gopalswamy et al., discloses a hydrodynamic coupling apparatus in the form of a vehicle torque transmission device including a magnetorheological clutch. Similarly, U.S. Pat. No. 6,334,832B1 issued 1 Jan. 2002 to Heravi et al. discloses a limited slip differential that uses “smart” control incorporating magnetorheological fluid. U.S. Pat. No. 6,371,267B1 issued 16 Apr. 2002 to Kao et al. discloses a liquid cooled magnetorheological fluid clutch that provides torque transfer between an engine and a transmission of a vehicle. U.S. Pat. No. 6,412,618B1 issued 2 Jul. 2002 to Stretch et al. discloses a particle clutch for which the amount of transfer force is determined by using magnetic particles or a magnetorheological fluid. United States Patent Application Publication No. US2002/0173400 and U.S. Pat. Nos. 6,428,441B1 and 6,527,664B2 issued 21 Nov. 2002 and 6 Aug. 2002, respectively, to Hunt disclose an electromagnetic clutch including a magnetorheological operator and a ball ramp operator. United States Patent Application Publication No. US2002/0119857 and U.S. Pat. No. 6,454,674B1 issued 24 Sep. 2002 to Krzesicki et al. disclose a controllable magnetorheological fluid-based torque limiting device for use with a vehicle differential. United States Patent Application Publication No. US2001/0041637 and U.S. Pat. No. 6,527,661B2 issued 4 Mar. 2003 to Leeper disclose a limited slip differential incorporating magnetorheological fluid brake elements. United States Patent Application Publication No. US2003/0134707 of Goldie et al. discloses a transmission having continuously variable speed ratios using magnetorheological clutch assemblies. United States Patent Application Publication No. US2003/0155201 of Bowen discloses a transfer clutch that includes a magnetorheological actuator. European Patent Document EP 940,286 discloses magnetorheological fluid clutches for use in vehicles in which torque transfer is modulated by controlling electrical signals to the coil to vary the viscosity of the magnetorheological fluid.
Each of the above patents teaches the use of closely-spaced flat disks or annuli that are immersed in magnetorheological fluid. When the magnetorheological fluid is exposed to magnetic flux, the magnetorheological fluid is at least partially solidified and the disks or annuli are coupled to each other through the magnetorheological fluid. A magnetic field directed through the disks or annuli and disposed normal to the surfaces of the disks or annuli and provides shear load support of the solidified or nearly solidified magnetorheological fluid between the adjacent surfaces of the disks or annuli. This system cannot transmit torque without shear load support of solidified or nearly solidified magnetorheological fluid. Without electrical power there is no appreciable torque transfer.
Also known are damping systems that control noise, vibration, and harshness (NVH) in a vehicle power train by using rubber element drives or added rotational inertia to “tune” the power train. However, a device such as this is only able optimize or tune a power train in a limited operating range. As the system deviates from the optimum tuned conditions, system response degrades.
What is needed is a magnetorheological hydrodynamic coupling apparatus capable of transmitting torque even when electrical power is removed from the field generator and that requires less electrical power for a given amount of torque transfer. What is also needed is a hydrodynamic damper capable of optimizing or tuning a power train throughout a broad operating range.